Unimodal dome-shaped island population of Ge/Si (0 0 1) by step-wise growth in UHV-CVD

This work introduces a new approach to achieve a unimodal dome-shaped island population for the self-assembled Ge/Si (0 0 1) dots grown by ultra-high vacuum chemical vapour deposition at T=620°C. A step-wise growth mode is applied, consisting of two Ge deposition steps with a short growth interruption in between. In the first step, a “base structure” with pyramids and domes is grown while in the second one, an additional Ge amount at reduced pressure is supplied. Selective “feeding” of only the pyramids and their conversion into domes occurs. Atomic force microscopy and transmission electron microscopy studies indicate that the shape transition starts with nucleation of material onto the {105} facets close to the most strain-relaxed top area of the pyramids.